fuel tank gauge doesn't work

[TxHorns]

my fuel tank gauge doesn't work and I'm trying to figure out what the problem is - any ideas on where I should start looking for the issue? In case you couldn't tell by the question, I'm fairly new to this stuff. Thanks guys.

 

[Texasmark]

Re: fuel tank gauge doesn't work

Fuel gauges work off 3 things: power/return, float level determining sending unit resistance, and dash gauge deflecting as a result of that varying current. Oh, and the gauge and the sending unit have to match. Probably by now there is a standard whereby the common sending unit resistance ranges produce 0 to full scale deflection on dash gauges.

Silvertip can nail the numbers for you and after I post this he will probably pick up on it as my response will send it back to the top.

The float varies the resistance in the tank to somewhere around 30 and 250 ohms between empty and full or full and empty....like I said, he knows which way it goes. Put 12v across that and the current in the circuit varies as V/R. That current is what causes the needle on the dash gauge to deflect.

With all that said, you still have the problem of the float accurately being at the top of the fuel for full and at the bottom of the fuel for empty. Usually, one (you personally) causes an empty reading to be displayed with some percentage of the fuel left in the tank for safety reasons.

Now you know how it works, look for what doesn't fit the senario.

Mark

 

[Bondo]

Re: fuel tank gauge doesn't work

- any ideas on where I should start looking for the issue?

Ayuh,... Find the tank's sending unit,...
Ground out the center wire from the gauge,.. It should peg Full...
If it don't, It's probably the gauge itself...
Or,..
It could be a Bad Ground at the tank...

If it Does,... change out the sender...

 

[stylesabu]

Re: fuel tank gauge doesn't work

Bond-o you're assuming all the wiring is good. so wouldn't it be best to check for voltage at sender 1st?

 

[Silvertip]

Re: fuel tank gauge doesn't work

Here's the typical fuel gauge wiring. Checking voltage at the sender proves nothing since voltage will be variable or nothing at all depending on the amount of fuel in the tank. Grounding the sender and pegging the gauge proves the wiring is ok and the sender is the culprit. Can't get much simpler than that. If grounding the sender doesn't change anything, disconnect the send wire and measure the resistance from the sender terminal to ground. Resistance will be 240 ohms empty, 109 ohms half full, and 33 ohms full. Do the math if the tank has a different amount of fuel and the numbers you get will vary a tad from those shown but not more than 10% or so. If the sender is good, then go up front. Look for 12 volts with key on at the + terminal of the gauge. Check for ground at the - terminal on the gauge. Disconnect the lead at the sender (S) terminal and measure resistance to ground. If it differs from what you measured directly at the sender you found the problem. Hint = its the send wire or its terminals. (That is if you followed the procedure in the order I just stated).

 

[Madbigdog2003]

Re: fuel tank gauge doesn't work

Silver Tip: I have a gas gauge issue also.....My gauge is pegged way past full at all times..(Like at 6:00)...The gauge fluttered when I first bought the boat, but now it is stuck on 6:00. My skeeter has two tanks and the when I switch between the tanks nothing happens it says on 6:00....What should I check first (Gauge/Wiring/Sender). And how should I go about it....

Thanks

Madbigdog2003

 

[seabob4]

Re: fuel tank gauge doesn't work

Silver Tip: I have a gas gauge issue also.....My gauge is pegged way past full at all times..(Like at 6:00)...The gauge fluttered when I first bought the boat, but now it is stuck on 6:00. My skeeter has two tanks and the when I switch between the tanks nothing happens it says on 6:00....What should I check first (Gauge/Wiring/Sender). And how should I go about it....

Thanks

Madbigdog2003

Check for continuity between the ground on the gauge and a known good ground. Highly unlikely both senders would have a bad ground.